<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width:300px;
            height:100px;
            border:1px solid black;
        }
        #div5{
            width:100px;
            height:50px;
            border:1px solid red;
           
        }
        #div1{
            /* margin:1px; */
            margin-bottom:10px;
            padding:10px;
        }
    </style>
</head>
<body>
    <div id="div1">
        <div id="div5">第一个div</div>
    </div>
    <div id="div2">第二个</div>
    <div id="div3">第三个</div>
    <div id="div4">第四个</div>

</body>
</html>